Method of forming glass having integral polarizing and non-polarizing regions

ABSTRACT

Method of making polarizing glass having integral polarizing and non-polarizing regions disclosed. The method involves applying a protective glass/frit material capable of blocking reducing gas to the surface of the glass to form a desired pattern, exposing the glass to a reducing gas atmosphere to render unprotected glass polarizing, and removing the protective glass/frit material to reveal underlying non-polarizing regions.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 09/173,892,filed Oct. 16, 1998, which also claims the benefit of U.S. ProvisionalApplication 60/063,741, filed Oct. 17, 1997.

BACKGROUND OF THE INVENTION

Well known methods exist for making polarizing glass. One suchcommercial method is by reducing silver or lead ions in a glass to theatomic state. For certain recent applications it has become desirable toprovide glass having both polarizing and non-polarizing regions integralthereto. While methods have been known for many decades for makingpolarizing glass, until recently, it had not been widely known thatpolarizing and non-polarizing glass regions can be made integral to asingle glass surface. Two such techniques have recently been disclosedin co-pending, co-assigned U.S. application serial nos. PCT/US 97/04870and 60/044,790 (both herein incorporated by reference), which havesuggested different approaches for forming polarizing regions innon-polarizing glass by photolithographic methods as well as byion-exchange methods.

The above recent techniques notwithstanding, there continues to be aneed for simpler and improved methods of producingpolarizing/non-polarizing glass. Accordingly, it is the object of thisinvention to provide a new and improved method for making polarizingglass regions in non-polarizing glass.

SUMMARY OF THE INVENTION

Briefly, the invention relates to a method of forming glass havingpolarizing and non-polarizing regions integral to the glass by providinga phase-separable, copper and silver-containing glass, said glass beingphase separable by virtue of the presence therein of silver-halideparticles; elongating the glass under stress such that the particles areelongated and aligned in the direction of the stress; applying aprotective material (frit barrier layer) to the surface of the glass toform a pattern of protected and unprotected regions, the frit materialbeing capable of blocking gases, in particular hydrogen to prevent suchgas from contacting the underlying glass; sintering the frit material;subjecting the glass to a reducing gas atmosphere to reduce thereducible phase in the unprotected regions of the glass and to therebyrender the glass in said regions polarizing; and removing the glass fritmaterial from the protected regions to reveal the underlyingnon-polarizing glass. The resulting glass is characterized by a patternof polarizing and non-polarizing regions.

DETAILED DESCRIPTION OF THE INVENTION

Any glass containing a reducible elongated phase such as, AgCl_(x)Br_(1-x), CuCl_(x) Br_(1-x), where x has a value between 0 and 1, orphase separated Pb-borate glass can be used for the present invention.Other useful reducible phases include, AgI, CuI and Cu/Cd halides. Oneexample of such glass is Corning's Photogray-Extra® glass described inU.S. Pat. No. 4,190,451, having a composition in weight percent on theoxide basis, of 0-2.5%, Li₂ O, 0-9% Na₂ O, 0-17% K₂ O, 0-6% Cs₂ O, 8-20%Li₂ O+Na₂ O+K₂ O+Cs₂ O, 14-23% B₂ O₃, 5-25% Al₂ O₃, 0-25% P₂ O₅, 20-65%SiO₂, 0.004-0.02% CuO, 0.15-0.3% Ag, 0.1-0.25% Cl, and 0.1-0.2% Br, themolar ratio of alkali metal oxide:B₂ O₃ ranging between about 0.55-0.85,where the composition is essentially free from divalent metal oxidesother than CuO, and the weight ratio Ag:(Cl+Br) ranges about 0.65-0.95.

To render such glass polarizing, the glass is first stretched orelongated under stress such that the silver or copper halide particlesare stretched or elongated and aligned in the direction of the stress.As described in the co-pending applications referenced above, thestretched glass containing elongated particles is then subjected to areducing gas treatment, an ion-exchange bath, or exposed to ultravioletlight and heat, to effect a reduction of the silver-halide particles andrender the glass polarizing.

We have discovered a relatively simple approach to forming a pattern ofpolarizing and non-polarizing regions on the glass by use of a fritglass slurry. Useful glass frits for the invention include borates andphosphates, in particular, borosilicate and borophosphate glasses suchas Corning's CF 1416 glass frit having a composition in weight percentbased on the oxides of: 10 wt. % B₂ O₃, 10 wt. % Al₂ O₃, 7 wt. % SiO₂,and 73 wt. % PbO. For best results, the frit glass preferably has acoefficient of thermal expansion in the range of 4×10⁻⁶ to 9×10⁻⁶. Ingeneral, the selected glass frit should have a coefficient of thermalexpansion that is as close as possible to that of the underlyingpolarizable glass.

In one illustrative example of this embodiment, silver-containing glasshaving a phase separable silver halide particles is coated with a glassfrit/photoresist mixture which is applied to the glass surface using anypractical method such as by spraying, stencil, doctor knife coating,screen printing, spin or dip coating. Preferably, the slurry shouldexhibit good flow viscosity, and be capable of forming a coating ofuniform thickness with little or no pinholes. The coated glass is thendried and exposed to ultraviolet radiation through a mask containing thedesired pattern of polarized/non-polarized glass. After exposure, theglass is developed to remove either the exposed or non-exposed fritmaterial (depending on whether a positive or negative photoresist isused), and heated to sinter the remaining glass frit materials. In anegative acting system, those areas of the photoresist which are exposedto ultraviolet light become insoluble in the developer solution so thatafter the unexposed areas have been developed, a negative image of theoriginal pattern is obtained. After the frit layer is sintered, theglass is subjected to a reducing gas treatment to reduce silver ions totheir atomic state and thereby polarize the glass. The sintered fritmaterial is then removed by any appropriate method such as by acidetching to reveal the underlying non-polarized glass. The resultingglass is thus characterized by a pattern of polarized and non-polarizedglass regions.

Examples of useful photoresist materials for forming the frit glassslurry include certain materials made by Shipley Inc., of Mass., andsold by Microelectronic Chemical Corporation, under the designations,S-1818, STR-1045, and S-1805.

Any solvent or solution which is capable of dissolving only theunreacted slurry can be used to develop the glass. Preferably, thedevelopment liquid is an aqueous solution such as dilute aqueouscarbonate solutions commonly used in the printed circuit-board industry,for example, aqueous sodium carbonate solution.

According to another embodiment, a mixture of frit and polymeric binderis applied to selected regions of the glass surface to form a barrierlayer in such regions. After applying the frit/polymer mixture to thesurface of the glass to form the desired structure, it is air dried,followed by heating at 380° C. for 15 minutes to remove the binder andexcess water. The samples are then fired at a temperature in the rangeof 420-500° C. (depending on the frit composition), for about 15 to 30minutes to sinter the frit.

Prior to sintering the frit thickness may be in the range of 20 to 60Tm. After the frit is sintered to form a glass layer, the thickness ofthe glass is generally in the range of 40 to 60% of the frit thickness.

After sintering, the glass is subjected to a reducing gas treatment topolarize the unprotected regions of the glass. The barrier layer is thenremoved to reveal underlying non-polarizing regions and to produce aglass having a pattern of polarizing and non-polarizing regions integralthereto. In this embodiment, the pattern of barrier material can beformed by any appropriate method. In a preferred embodiment the mixtureof frit and polymer material is applied by spray, screen, and stencilprinting methods onto the glass surface through a plate having thedesired pattern.

The glass frit/binder mixture preferably includes at least 40 wt % glassfrit, 5 to 10% binder, the balance being water. Depending on the type ofbinder, it may be beneficial to add other solvents such as alcohols inorder to increase the solubility of binder. Also, for improvedwettability, a surfactant may be added. Generally, the lower the fritcontent, the lower the viscosity and the lower the fired thickness ofthe barrier layer.

Examples of useful binders and adhesives for making the frit slurryinclude Aquazol® a poly (2-ethyl-2-oxazoline) available from PolymerChemistry Innovations, Arizona, and amyl acetate nitrocellulosesolutions.

EXAMPLES

1. To demonstrate the gas-blocking effect of the frit/binder of theinvention, ten grams of frit glass Code 1416 purchased from Ferro, Inc.was mixed with 25 cm³ of amylacetate nitrocellulose (binder) and themixture was left on roller mixture overnight for proper mixing. Severalsamples of Corning's Glass Code 8111 (a phase separable, copper andsilver-containing glass characterized by elongated silver halideparticles, also available from Corning Incorporated, Corning, N.Y.) werecut to 1"×3" dimensions. A small region measuring 1"×0.5" was masked offin each sample using a tape. The unmasked regions of the glass sampleswere then dip-coated with the frit/binder mixture. After coating, thesamples were air dried at room temperature, the tape was removed and theglass was then placed in an oven and heated at 380° C. for 15 minutes toremove the binder. Finally, the samples were fired to a temperature of500° C. at the rate of about 10° C./minute and held at 500° C. for 15minutes. The heated frit flowed and formed a glass layer having athickness in the range of 12-15 m on the stretched glass surface. Afterthe frit layer was formed on the glass surface, the glass samples, alongwith several control samples (uncoated Code 8111 glass), were heated ina hydrogen reduction furnace for six hours.

After the hydrogen treatment the frit layer was removed by acid etching.We observed that the glass underlying the coated regions of the sampleswere not affected by the hydrogen treatment as they retained theoriginal color of the Code 8111 glass, indicating the frit glass waseffective in blocking the reducing gas (in this case, hydrogen), andfrom preventing the gas from contacting the underlying glass. Theunprotected glass region was observed to be polarized by the hydrogentreatment.

2. In the following example, we illustrate one embodiment of theinvention in which a pattern of polarizing glass is formed on anon-polarizing glass by means of a photolithographic process.

(a) Slurry. A 250 ml Nalgene bottle was duct-taped to prevent theentrance of UV light, and 10 pieces of ceramic media mixing balls wereplaced in the bottom of the bottle; 140 g of Corning Glass Code CF1416frit glass powder was weighed into the bottle; 70 g of SC1805 Shipleyphotoresist was measured and added to the frit in the yellow light cleanroom; the cap was sealed with duct tape and the mixture placed on theroller mixture overnight to obtain a uniform slurry mixture.

(b) Coating/Drying. Sample spraying was carried out in a clean roomusing an air regulator set at 30 psi and a small Bink spray gun. Theglass samples were coated with a single pass spray of the frit glassslurry of 2(a) above. The sprayed samples were dried in a 90° C. ovenfor 15 minutes.

(c) UV Exposure. Three frit glass-sprayed samples were exposed to UVlight for 5, 10, and 15 seconds respectively. The samples exposed for 15seconds gave the most satisfactory results. Precise, well-rounded,sharp-edged circles were evident in the pattern at 50X magnification.After exposure, the samples were developed using a 5:1 mixture ofdeionized water/351 Shipley Developer. The 5 and 10 second samplesrequired scrubbing to remove exposed frit/photoresist. Afterdevelopment, the samples were rinsed with deionized water, air dried,and then dried in a 90° C. oven for 15 minutes. Dektak measurementsshowed an average pattern thickness of about 10 microns. Finally, thebacks or reverse sides of the samples were sprayed with about 10 micronsthick frit glass.

(d) Sintering. Sintering was done by placing samples in a roomtemperature oven, ramping at 10° C./minute to a top temperature of 500°C. for 15 minutes, then ramped down to room temperature.

(e) Hydrogen Treatment. The sintered samples were subjected to ahydrogen environment for 5.5 hours at 3 atmospheres to reduce theexposed regions of the glass and thereby polarize such regions. Afterthe reduction process, the samples were cleaned in 20% acetic acid toremove the frit glass. Microscopic inspection of the samples showed apattern of well rounded non-polarizing circles.

The following examples illustrate the use of silk screen and stencilprinting techniques to produce 2.45 mm diameter frit images and solidfrit on clear glass slides for the purpose of blocking hydrogen in thefinal firing stage.

Silk Screen Dot Printing Process

a) a dark field, quartz glass with a 90 dot pattern was used as aworking master to photographically produce a film positive which wasthen used to produce a 400 mesh stainless steel silk screen on a 12" by12" support frame;

b) the silk screen was coated with 10 micron thickness of HP emulsion;

c) two media were produced with frit for subsequent printing of thepattern through the silk screen; the first medium was produced usingpine oil, and then roll-milled with CF-1416 frit to a final viscosity ofabout 80,000 cps while the second medium, IP-9025W, available fromHeraeus Corporation was used at a viscosity of 96,000 cps. IP-9025W isessentially a mixture of terpineol, bi-butyl phthalate, and glass frit.

d) the patterns were printed with a screen printer using the 400 meshstainless steel silk screen and the two printing media. The screenprinter was fitted with a 60 durometer squeegee and flood bar andoperated at a speed of 2.5 inches per second.

e) the clear glass samples were then fired at 500° C. and evaluated.

Silk Screen Solid Printing Process

a) a rubylith master positive with a pattern of 36 mm by 76 mm wasproduced;

b) a 400 mesh stainless steel silk screen having the same solid patternwas silk screen printed on clear glass with a screen printer usingCERDEC 479 oil with CF1416 frit, and IP-9026W media as described above.The pattern was also screen printed using a mixture of Shippley STR-1045Photo Resist with CF-1416 frit and exposed with a UV source to producethe dot pattern by photolithography;

c) the clear glass was then fired at 500° C. and evaluated.

Stencil Printing Process

a) dot pattern was digitized on a computer file which was used to laseretch a 0.002" and 0.003" thick stencil;

b) several media were produced using (i) Heraeus IP-9025W at 96,000 cps,(ii) Heraeus IP-9026 at 112,000 cps and (iii) Heraeus IP-9039 at 220,000cps;

c) the pattern was stencil printed on clear glass and Corning'sPolarcor® glass with a printer fitted with a stainless steel squeegeeand flood bar with operating speeds of 1 to 5 inches per second;

d) the samples were then fired at 500° C. and evaluated for printquality.

What is claimed is:
 1. A method of forming glass having polarizing andnon-polarizing regions integral thereto, the method comprising the stepsof:a) providing a phase-separable glass containing a metal halidereducible phase selected from the group consisting of copper halide andcadmium halide; b) elongating the glass under stress to elongate andalign the metal halide phase in the direction of the stress; c) applyingin the form of glass/frit mixture, a protective material to the surfaceof the glass to form a pattern of protected and unprotected regions,said protective material being capable of blocking a reducing gas; d)subjecting the glass to a reducing gas atmosphere to reduce thereducible elongated metal halide phase in the unprotected regions of theglass and thereby render the glass in said regions polarizing; and (e)removing the protective material from the glass to reveal underlyingnon-polarizing glass.
 2. The method of claim 1 further comprising thestep of sintering the protective material prior to step (d).
 3. Themethod of claim 2 wherein the protective material is sintered at atemperature in the range of 420 to 500° C.
 4. The method of claim 3wherein the protective material is sintered in the presence of hydrogenand oxygen.
 5. The method of claim 1 wherein the protective material isselected from the group consisting of glass/frit and binder; photoresistand glass/frit; and combinations thereof.
 6. The method of claim 5wherein the glass frit comprises low-forming temperature glass fritsselected from the group consisting of borosilicates, phosphates andborophosphates.
 7. The method of claim 6 wherein the glass frit isselected from the group consisting of lead-borosilicates,lead-zinc-phosphates, and lead-zinc-borates.
 8. The method of claim 7wherein the glass frit comprises in weight percent based on oxides of:10 wt. % B₂ O₃, 10 wt. % Al₂ O₃, 7 wt. % SiO₂, and 73 wt. % PbO.
 9. Themethod of claim 1 wherein the protective material comprises, ZnO and/orCuO, in combination with a binder, and/or B₂ O₃.
 10. The method of claim9 wherein the binder is selected from the group consisting ofpoly(2-ethyl-2-oxazoline) and amylacetate nitrocellulose.
 11. The methodof claim 1 wherein the protective material is removed by acid etching.12. The method of claim 1 wherein the protective material comprises amixture of glass frit and photoresist.